1. Field of the Invention
The present invention relates to sonar transducers. More particularly, the invention relates to an ultrasonic sonar transducer that more effectively transmits and receives sonar signals even when the water vessel to which it is attached is traveling at high speeds.
2. Description of the Prior Art
Sonar transducers are commonly used in depth finder and fish finder systems for determining the depth of a body of water or for locating underwater objects such as fish and fish beds. Sonar transducers are typically either integrally formed as a part of a water vessel hull or mounted behind the water vessel by suitable brackets.
Sonar transducers that are configured for attachment to a water vessel typically include a transducer element for transmitting and receiving acoustic energy (sonar) and a transducer housing for enclosing or housing the transducer element. To provide optimal performance, it is important that transducer housings be mounted so that they are at least partially underwater so that the sonar is delivered from the transducer element directly into the water without first passing through the air above the water. However, those skilled in the art will appreciate that such underwater mounting causes undesired turbulence and cavitation, especially when the water vessel to which the sonar transducer is attached is traveling at high speeds. Turbulence and cavitation in turn cause attenuation and reflection of the transmitted and received acoustic energy and thus interfere with operation of the sonar transducers.
These turbulence and cavitation problems are exasperated by known prior art sonar transducer designs which have transducer housings with flat bottoms. Flat bottoms create excessive turbulence and cavitation and therefore cause signal attenuation and reflection as described above. Prior art sonar transducers also typically have sharp corners that further lead to additional undesired turbulence and cavitation. To reduce cavitation in these types of prior art sonar transducers, it is known to mount the transducer housings at a slight positive angle of attack (i.e. the front of the housings raised) relative to the oncoming water. This is partially effective at reducing turbulence and cavitation, but the angling of the transducer housings also angles the transducer elements contained in the housings so that the transducer elements are no longer parallel to the surface of the water. This causes the transmitted and received acoustic energy to travel at angles relative to the surface of the water and therefore distorts target images and reduces the accuracy of depth measurements.
The present invention solves the above-described problems and provides a distinct advance in the art of sonar transducers. More particularly, the present invention provides a sonar transducer that more effectively transmits and receives sonar signals even when the water vessel to which it is attached is traveling at high speeds.
In one preferred embodiment of the invention, the sonar transducer includes a transducer element and a transducer housing for housing the transducer element. The transducer housing includes a lower housing section having a bottom wall that is continuously curved with no major portion thereof parallel to the bottom face of the transducer element. The curved bottom is preferably bow-shaped so that the front of the transducer housing is raised relative to the rear to create a positive angle of attack relative to the oncoming water. This pressurizes water flow under the bottom of the transducer housing and promotes a laminar flow. Such a laminar flow reduces turbulence and cavitation and therefore nearly eliminates undesirable attenuation and reflection of transmitted and received energy. Although the transducer housing bottom is curved, the bottom face of the transducer element remains parallel to the surface of the water so that sonar is transmitted and received perpendicular to the surface of the water.
In another embodiment of the present invention, the transducer housing includes an acoustic window aligned with the bottom face of the transducer element for passing acoustic energy into and out of the transducer housing. The acoustic window is preferably formed from a combination of a recessed portion in the bottom wall and potting material positioned between the bottom face of the transducer element and the recessed portion.
The recessed portion of the bottom wall and the potting are preferably formed of material having a specific gravity approximately equal to the specific gravity of water. The combined thickness of the recessed portion and the potting material is preferably approximately equal to one half of the wavelength or an integer multiple of one half of the wavelength of the acoustic energy transmitted by the transducer element. The combination of these two factors makes the acoustic window nearly transparent to the acoustic energy transmitted from the transducer element.
These and other important aspects of the present invention are described more fully in the detailed description below.